This invention is directed to an improvement in the Strickland "bulk air" invention set forth in U.S. Pat. No. 3,905,790 ("Strickland patent") which discloses the preparation of fibers of glass by drawing molten glass through an orifice plate. The description of the "bulk air" system of the Strickland patent is incorporated herein by reference. The Strickland "bulk air" invention contemplates passing separate streams of molten glass formed at each orifice, while directing a bulk flow of rapidly moving gas upwardly to the orifice area of the orifice plate, this bulk flow constituting a generally single gas column at the cone and plate area of the orifice plate. This Strickland "bulk air" flow cools the cones of glass to provide a stable cone formation and to maintain a separation of cones thereby preventing flooding. With a flow of bulk air upward to the orifice plate even with a relatively diminished volume of air less than in the preferred embodiments of the Strickland patent, it is believed that such bulk air impinges on the orifice plate to eliminate stagnant gas adjacent the orifice plate, with the gas moving outwardly in all directions from the orifice area. The Strickland bulk air also supplies a source of gas sucked downwardly by the fibers as they are attentuated from below, the bulk air substantially eliminating ambient gas drawn into the region of the fiber cones. Any mechanical arrangement may be used to provide the bulk air, it being important that when the air reaches the cone area of the orifice plate, it arrives as a generally single upwardly moving air column. Various mechanical arrangements for providing such bulk air are disclosed in detail in the Strickland patent.
The Strickland invention may also be described as providing a method of blowing air toward the undersurface of the orifice plate in countercurrent relationship to the glass fiber streams being drawn from the orifice plate. In accordance with this method, even when the orifice plate has such a high density of orifices as to cause the coalescence of adjacent molten glass cones and the resultant flooding of the undersurface of the orifice plate in the absence of the bulk air, the air blown against the undersurface of the orifice plate serves not only to cool the molten glass cones but also to expel gases stagnant around them. The strong cooling effect achieved by the Strickland "bulk air" invention avoids the need for cooling fins or cooling water circulation pipes, and permits an orifice density higher than that with previous tipped orifice plates. The orifice plate employed in the Strickland invention generally has a thickness of from 1.0 to 10 mm and 2,000 to 6,000 orifices. There is generally an orifice spacing of from 1.40 mm to 4.00 mm; such an orifice plate is referred to herein as a "closely spaced orifice plate".